Blood oxygenation level dependent (BOLD) fMRI has generated an enormous amount of interest among neuroscientists, nuclear magnetic resonance scientists, and clinicians. It has rapidly become an important tool for studying neuronal activities in the human brain. However, despite various successful applications, the ability to detect task related changes by fMRI is potentially limited by signal fluctuations unrelated to the neuronal activation under investigation. In particular, it has been recognized that signal intensities in images are susceptible to physiological motions including respiration and cardiac pulsation. To improve the sensitivity of fMRI and to broaden its application, it is important to understand how the signals in fMRI vary with physiological motions and to develop means to compensate for these variations. Therefore, the overall goal of this project is to understand and reduce physiological fluctuations in fMRI and to demonstrate the improvement in fMRI with reduction of physiological fluctuation. Specifically, the proposed project will develop new methods for monitoring and compensating signal fluctuations related to respiration and cardiac pulsation in functional imaging data, validate the improvement with receiver operating characteristic analysis and reliability test, and assess and optimize various imaging sequences utilized for fMRI based on an objective assessment of signal contrast and physiological fluctuation using the techniques developed for physiological fluctuation monitoring. The improvement to be made in this project will be utilized to more sophisticated neuronal systems, including the olibocerebellar system, in the future.